Field of the Invention
This invention relates to a method of soil sterilization to control undesirable biotica resident therein, such as weeds, nematodes, spores and fungi, in open tillable soil areas and more particularly to soil sterilization by the application of gamma rays to the tillable areas.
There has been a long felt need for an effective method of controlling undesirable biotica in tillable soils which does not have adverse ecological consequences. While undesirable vegetation and pests may be controlled by the application of chemicals such as pesticides and herbicides, these chemicals leave harmful residues which may persist for long periods of time and lead to unacceptable buildups of breakdown products in those animals at the top of the food chain.
Other present day methods include mechanical devices and controlled burning. The mechanical devices are either ineffective or are expensive to apply. It is also difficult to use a mechanical method such as cultivation in rainy seasons, and such cultivation can contribute to soil erosion. Controlled burnings generally result in an unacceptably high level of environmental pollution.
It has been proposed to control undesirable vegetation in tillable areas by the application of microwave energy thereto. U.S. Pat. No. 4,092,800 proposes applying energy at an output frequency of 300 megahertz to 300 gigahertz to achieve vegetation control. A method for carrying out the application of the microwave energy involves generating an electromagnetic wave of the appropriate frequency, subjecting an area within which vegetation is to be controlled to the electromagnetic wave emission, and reflecting the wave emission after it has passed through the area back into the area of vegetation control to achieve an energy density in the range of 150 Joules/cm.sup.2 to approximately 300 Joules/cm.sup.2. It is claimed that microwave energy of this energy density is sufficient to cause the death or debilitation of the vegetation without raising the temperature of the soil to undesirable levels.
While microwave energy can be used to control vegetation, this method is effective only if either the energy density of the microwaves is very high or if the microwaves are applied to a particular area for time periods as long as 32 seconds. Thus, the method disclosed in U.S. Pat. No. 4,092,800 is impractical because of the excessively high energies or long time periods required to achieve lethal dosages.
Thus, it would be desirable to provide control of undesirable biotica in the soil which involves neither the environmental dangers posed by chemical pesticides or controlled burning, or the expense and impractibility of mechanical methods. It would also be desirable to use electromagnetic energy of a frequency such that brief application of the energy would achieve satisfactory results.